Quantum dots are defined as small particles whose linear dimension in all three directions is less than the de Broglie wavelength of the electrons or holes. Such particles have a greatly modified electronic structure from the corresponding bulk semiconductor material and, in particular, the density of states becomes more like that for molecules. The applications for quantum dots are generally in the field of optoelectronics, and includes such things as light switches and light emitters. A paper describing quantum dots and some of their properties has been published in Angewandte Chemie International Edition (English) 1993, 32, at pages 41-53: "semiconductor q-particles: chemistry in the transition region between solid state and molecules" by Horst Weller.
For the successful exploitation of quantum dots, it is important that all or most of the particles are of the same physical size and shape. With improved consistency of particle size and shape the materials made from such particles have well defined excitonic features which in turn improves the responsiveness and efficiency of optoelectronic devices utilising such materials. A number of methods of achieving this has been tried and most are centred on the production of colloids or inverse micelles or on "smokes". Size control or size selection remains a problem and is the subject of a great deal of research effort. This invention offers a new approach to this problem which may be capable of giving up to about an order of magnitude better size control.
In one aspect, the invention provides a method of making particles of substantially uniform size of a metal or metal compound, which method comprises providing a solution in an evaporable solvent of the metal in chemically combined form, forming the solution into droplets of substantially uniform size, contacting the droplets with a gas-phase reagent so as to form the metal or metal compound, and removing the evaporable solvent from the droplets.